The present invention relates to a material for liquid keeping containers which is excellent in impact resistance, chemical resistance and water vapor transmission resistance and suitable for molding liquid keeping containers such as automobile parts of anti-freezing system, such as radiator tanks, and battery cases for secondary batteries, and to a liquid keeping container comprising a molded product of the material.
At present, thermoplastic resins are used for radiator tanks which are automobile parts, taking into consideration their lightness and easiness in processability. For using thermoplastic resins for radiator tanks, they are required to have performances such as impact resistance, chemical resistance and water vapor transmission resistance. For example, coolant used for cooling engines is circulated at about 100xc2x0 C. at steady state, but the temperature thereof rises instantaneously to about 130xc2x0 C. when the engine is stopped. Therefore, thermoplastic resins used for radiator tanks must have not only chemical resistance to stand the coolant at high temperatures, but also water vapor transmission resistance to prevent decrease of the amount of coolant caused by volatilization of water contained in the coolant. Furthermore, they are needed to have impact resistance for improving safety against breakage caused by shock. The materials used at present are polyamide resins, which are usually reinforced with glass fibers (GF). The GF-reinforced polyamide resins are superior in heat resistance and water vapor transmission resistance, but have the defect that they undergo hydrolysis with coolant liquid of high temperatures to result in deterioration of strength. Moreover, with recent progress in performance of engines, the coolant tends to be further heated, and the conventional polyamide resins do not meet the requirement, and materials having long-term stability to be substituted for the polyamide resins have been demanded.
Moreover, with recent spread of portable telephones, personal computers, video cameras and electric cars, rechargeable secondary batteries are noticed. In order to use the resins for battery cases as containers for the batteries, they are also required to have performances such as impact resistance and chemical resistance. That is, they are needed to have the chemical resistance for preventing damage on the peripheral devices caused by leakage of organic electrolyte used and the impact resistance for improving safety against breakage caused by shock. Furthermore, water vapor transmission resistance is also needed depending on the kind of the secondary batteries.
There are various resin materials, but, at present, no materials are known which satisfy all of the performances such as water vapor transmission resistance, heat resistance, impact resistance and chemical resistance suitable for the above uses.
The objects of the present invention is to provide a material which is excellent in water vapor transmission resistance, chemical resistance, heat resistance and mechanical strength and suitable for liquid keeping containers, e.g., automobile parts of anti-freezing system such as radiator tanks and battery cases for secondary batteries, and to provide a liquid keeping container comprising a molded products of said material.
As a result of research conducted by the inventors in an attempt to solve the above problems, it has been found that a resin blend composition which contains a syndiotactic polystyrene resin excellent in heat resistance and markedly excellent in chemical resistance and a polypropylene resin and has a two-phase structure comprising a polypropylene resin phase and a syndiotactic polystyrene resin phase is excellent in water vapor barrier properties, good in heat resistance and chemical resistance and excellent in mechanical strengths such as impact resistance and shows substantially no deterioration in properties even when it is dipped in a special liquid such as an anti-freezing solution mainly composed of ethylene glycol at a high temperature for a long time, and, therefore, is most suitable as a material for liquid keeping containers such as automobile parts of anti-freeze system which are required to have water vapor transmission resistance, heat resistance, chemical resistance and impact resistance. Thus, the present invention has been accomplished.
That is, the present invention relates to a material for liquid keeping containers which comprises a resin composition containing a syndiotactic polystyrene resin and a polypropylene resin and also having a compatibilized structure of a syndiotactic polystyrene resin phase and a polypropylene resin phase, the proportion of these phases being 90-10/10-90 (weight ratio), and further relates to a liquid keeping container comprising a molded product of said material.
The present invention further relates to a material for liquid keeping containers which is excellent in mechanical strength and which contains a thermoplastic elastomer, a polyphenylene ether resin and/or an inorganic filler in addition to the above composition, and further relates to a liquid keeping container comprising a molded product of said material.